1. Field of the Invention
This invention relates in general to serial communications systems, and more particularly to a generic label encapsulation protocol for carrying label switched packets over serial links.
2. Description of Related Art
Demand for bandwidth is skyrocketing in data service provider networks. With this demand comes a need for efficient bandwidth utilization, higher performance and simplicity. Fullest traffic an Internet Protocol (IP) traffic volumes are expected to continue to increase at substantially higher rates. With the rise of IP throughout global networks, many high volume links are trying to sidestep the additional burden required by ATM cells. Most carriers use SONET (Synchronous Optical Network) as the OSI layer I specification for data transmission over optical fibers in the public network, and ATM is then used as the OSI layer II link. However, the extra data that must be added to a packet to traverse an ATM link can eat up more than 10 percent of ATM's raw bandwidth. Further, there are many other packet protocols for bundling data for transmission. While SONET will be mentioned herein as a primary example, those skilled in the art will recognize that the concepts discussed here are valid for any serial link.
SONET is a family of transmission rates from 51.84 Mbps (the base rate) to 13.22 Gbps that was created to provide the flexibility needed to transport many digital signals with different capacities, and to provide a design standard for manufacturers. Despite the name, it is not limited to optical links. SONET development began as a suggestion to the Exchange Carriers Standards Association and ultimately came to rest at the American National Standards Institute (ANSI). SONET has also been adopted by the International Telecommunications Union--Telecommunications Standardization Sector (ITU-T). The ITU-T version is know as Synchronous Digital Hierarchy (SDH), which varies slightly in that SDH levels begin at 155 Mbps.
To deliver efficient network manageability and scalability, today's data networks are based on a hierarchical architecture that includes the backbone as well as the service node layers. The major function of a router and a backbone is to provide performance and scalability, to switch millions of packets per second, and to scale to high rates. At the service nodes or the distribution layer, the main goal of an edge router is to provide features such as security access control, and support for differentiated services through class of service (CoS) offering. For example, most carriers transport their router traffic through the SONET/SDH platforms for long distances. The SONET/SDH hardware forms the main infrastructure amending telecommunication providers and enterprises worldwide. Therefore, it is imperative for the data equipment to inter operate with this infrastructure seemlessly.
IP over SONET/SDH is gaining popularity as a way to reduce the ATM overhead burden described above and squeeze more bandwidth out of a link. IP over SONET/SDH removes ATM from the transmission picture, foregoing the traditional method of encapsulating IP packets into an ATM cell, which is then mapped into a SONET frame. Instead, this technology maps the IP package straight into a SONET frame.
Packet data over SONET/SDH is the servo transmission of data over SONET frames through the use of point-to-point protocol (PPP). PPP was designed as a standard method of communicating over point-to-point links. Initial deployment was designed for short local lines, lease lines and plain-old-telephone-service (POTS) using modems. As new packet services and higher speed lines are introduced, point-to-point protocol is easily deployed in these environments as well.
PPP treats SONET transports as octet oriented synchronous links. PPP presents an octet interface to the physical layer and there is no provision for sub-octets to be supplied or accepted. The octet stream is mapped into the SONET synchronous payload envelope (SPE), with the octet boundaries aligned with the SPE octet boundaries. SONET provides substantial overhead information, allowing simpler multiplexing and greatly expended operations, administration, maintenance and provisioning (OAM&P) capabilities.
SONET includes multiplexing principles such as mapping, aligning, multiplexing and stuffing. One of the benefits of SONET is that it can carry large payloads (above 50 Mbps). Nevertheless, the digital hierarchy signals can be accommodated as well by subdividing STS (Synchronous Transport Signals) SPE into smaller components of structures known as virtual tributaries (VTs), for the purpose of transporting and switching payloads smaller than the STS-1 rate.
Accordingly, packet over SONET/SDH is an ideal feature for networks that are built for providing Internet or IP data. Packet over SONET/SDH provides superior bandwidth utilization and efficiency over other transport methods. However, not all networks can reap the benefits of IP over SONET/SDH. First, all data traversing the link must be IP. Because 155 Mbps over IP data is not easy to come by, this requirement is a major drawback of using IP over SONET/SDH. ATM can be more easily statistically multiplexed than IP over SONET/SDH. However, ATM can be run on lower speed links. But, as mentioned above, ATM carries the additional overhead that must be added to each packet to traverse the ATM link.
As the convergence occurs towards delivery of audio, data, images and video through diverse transmission switching systems that supply high speed transportation over any medium to any location, SONET is gaining momentum as the transport network for transmitting packets due to its reduced overhead compared to IP over ATM-type solutions. However, as stated above, the current approach is directed to packet over SONET/SDH using point-to-point protocol encapsulation.
There is an ongoing effort in the IETF to provide easy switching for packet traffic over servo links by using labels and label switching routers (LSR). The multi-protocol label switching (MPLS) groups work is directed at solving the complexity involved in label-switching and presenting a standard-based interoperability testing proposal. Label switching adds connections to connectionless protocols such as Transport Control Protocol/Internet Protocol (TCP/IP). By calculating routes across the network and assigning "tags" or "labels" to those routes, frame forwarding is simplified to the point where it also can be implemented in hardware. Given this architecture, labels switching can, in theory, operate equally well over ATM and non-ATM environments. In ATM networks, the label already exists; it is the virtual channel (VC) address. In non-ATM environments, such as Ethernet, new protocols have to be developed to accomplish this. The main advantage of using labels is improved forwarding capability to elimination of layer three look-up and the traffic engineering capabilities brought by the use of labels.
However, as mentioned above, the only approach currently used for carrying packet traffic over SONET/SDH uses point-to-point encapsulation. A definition as to how labels can be encapsulated has not yet been proposed. Further, even if labels are used for carrying packet traffic over servo links, the problem of detecting the end of packet without having to look inside the payload has now been solved.
It can be seen then that there is a need for encapsulation for carrying label switch packet over servo links.
It can be seen then that there is a need for a method to detect the end of packets without having to look inside the payload.